The invention relates generally to medical imaging, and more particularly to a system and method for aligning a medical image of a brain to a reference atlas.
There are a variety of medical imaging systems that are currently in use that are capable of producing images of the internal anatomy of a patient. In addition to conventional X-ray machines, several technologies have been developed in recent decades that enable three-dimensional medical image data to be stored digitally. The medical image data may then be used to generate two-dimensional medical images from a variety of different perspectives. Typically the information is presented as cross-sections, or slices, of a patient's body, such as the brain.
Computed tomography (CT) is an example of a medical imaging technique that uses X-rays to create and store medical image data in three-dimensions. The patient in inserted into an aperture in a CT imaging system. An X-ray source and an X-ray detector are located on opposite sides of the patient. The X-ray source and X-ray detector are spun around the patient, while the CT imaging system takes a series of X-ray images of the patient. The CT imaging system has a computer program that uses a set of algebraic equations to estimate how much of the X-ray beam produced by the X-ray source is absorbed in the patient's body. As an approximation, the denser a material is, the whiter a volume of it will appear on the scan. Each X-ray image contains two-dimensional medical image data However, the CT imaging system is able to incorporate the two-dimensional image data and combine it in a way to form a three-dimensional model of the patient. A user may then select a desired slice (cross-section) of the three-dimensional model of the patient to be produced as a medical image. The slice may be taken at any angle relative to the body.
Magnetic resonance (MR) imaging is another imaging modality that is used to visualize the internal anatomy of a patient. However, MR imaging systems use magnetic fields, with radio frequency pulses to create images. MR is primarily used to look for structures, alterations or damage in soft living tissues, like the gray and white matter of the brain. MR imaging systems also have the ability to store imaging data in three-dimensions and for multiple slices, so that medical images of selective slices of a patient may be produced.
Each of these medical imaging methods has their various strengths and weaknesses. For example, CT systems are very good at producing images of bone, but are less useful at producing images of certain soft tissues, such as the brain. MRI systems, on the other hand, are very good at producing images of soft tissues, but are somewhat less available and can take much longer to produce an image than a CT system.
In addition, MR images of the brain are easily referenced to the Talairach atlas. The Talairach atlas is a three-dimensional coordinate system that is used to describe the location of brain structures independent of individual differences in the size and overall shape of the brain. The Talairach atlas uses the anterior commissure and the posterior commissure of the brain as reference points. The anterior and posterior commissures are fiber tracts that connect the two hemispheres of the brain. However, these anatomical features are not visible on CT images. Furthermore, there are certain risks and counter-indicators that are associated with the use of MR systems (namely as a result of the strong magnetic field that they produce) that preclude or discourage their use when the patient is unconscious, incoherent or otherwise unable to respond to questions.
Therefore, a need exists for a system or method that enables a CT system to have some of the additional benefits of an MR system without the drawbacks associated with their use.